linux-kernel - Re: [PATCH 1/2] x86/CPU: Use correct macros for Cyrix calls on Geode processors

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Message-ID: <CAHP3WfOgs3Ms4Z+L9i0-iBOE21sdMk5erAiJurPjnrL9LSsgRA@mail.gmail.com>
Date: Tue, 24 Dec 2024 04:17:50 -0800
From: Russell Senior <russell@...sonaltelco.net>
To: Matthew Whitehead <tedheadster@...il.com>
Cc: linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...nel.org, 
	luto@...nel.org, Jonas Gorski <jonas.gorski@...il.com>
Subject: Re: [PATCH 1/2] x86/CPU: Use correct macros for Cyrix calls on Geode processors

More poking/prodding and coaching from Jonas Gorski (cc'd), it looks
like this test patch fixes the problem on my board: Tested against
v6.6.67 and v4.14.113:

--- a/arch/x86/kernel/cpu/cyrix.c
+++ b/arch/x86/kernel/cpu/cyrix.c
@@ -153,8 +153,8 @@ static void geode_configure(void)
        u8 ccr3;
        local_irq_save(flags);

-       /* Suspend on halt power saving and enable #SUSP pin */
-       setCx86(CX86_CCR2, getCx86(CX86_CCR2) | 0x88);
+       /* Suspend on halt power saving */
+       setCx86(CX86_CCR2, getCx86(CX86_CCR2) | 0x08);

        ccr3 = getCx86(CX86_CCR3);
        setCx86(CX86_CCR3, (ccr3 & 0x0f) | 0x10);       /* enable MAPEN */


On Mon, Dec 23, 2024 at 5:04 PM Russell Senior
<russell@...sonaltelco.net> wrote:
>
> Hi,
>
> I still have some Soekris net4826 in a Community Wireless Network I
> volunteer with. These devices use an AMD SC1100 SoC. I am running
> OpenWrt on them, which uses a patched kernel, that naturally has
> evolved over time.  I haven't updated the ones in the field in a
> number of years (circa 2017), but have one in a test bed, where I have
> intermittently tried out test builds.
>
> A few years ago, I noticed some trouble, particularly when "warm
> booting", that is, doing a reboot without removing power, and noticed
> the device was hanging after the kernel message:
>
>   [    0.081615] Working around Cyrix MediaGX virtual DMA bugs.
>
> If I removed power and then restarted, it would boot fine, continuing
> through the message above, thusly:
>
>   [    0.081615] Working around Cyrix MediaGX virtual DMA bugs.
>   [    0.090076] Enable Memory-Write-back mode on Cyrix/NSC processor.
>   [    0.100000] Enable Memory access reorder on Cyrix/NSC processor.
>   [    0.100070] Last level iTLB entries: 4KB 0, 2MB 0, 4MB 0
>   [    0.110058] Last level dTLB entries: 4KB 0, 2MB 0, 4MB 0, 1GB 0
>   [    0.120037] CPU: NSC Geode(TM) Integrated Processor by National
> Semi (family: 0x5, model: 0x9, stepping: 0x1)
>   [...]
>
> In order to continue using modern tools, like ssh, to interact with
> the software on these old devices, I need modern builds of the OpenWrt
> firmware on the devices. I confirmed that the warm boot hang was still
> an issue in modern OpenWrt builds (currently using a patched linux
> v6.6.65).
>
> Last night, I decided it was time to get to the bottom of the warm
> boot hang, and began bisecting. From preserved builds, I narrowed down
> the bisection window from late February to late May 2019. During this
> period, the OpenWrt builds were using 4.14.x. I was able to build
> using period-correct Ubuntu 18.04.6. After a number of bisection
> iterations, I identified a kernel bump from 4.14.112 to 4.14.113 as
> the commit that introduced the warm boot hang.
>
>   https://github.com/openwrt/openwrt/commit/07aaa7e3d62ad32767d7067107db64b6ade81537
>
> Looking at the upstream changes in the stable kernel between 4.14.112
> and 4.14.113 (tig v4.14.112..v4.14.113), I spotted a likely suspect:
>
>   https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=20afb90f730982882e65b01fb8bdfe83914339c5
>
> So, I tried reverting just that kernel change on top of the breaking
> OpenWrt commit, and my warm boot hang went away.
>
> Presumably, the warm boot hang is due to some register not getting
> cleared in the same way that a loss of power does. That is
> approximately as much as I understand about the problem.
>
> Can you suggest a patch to try to either clarify what is going wrong
> and/or to potentially fix the problem in a more appropriate way?
>
> Thanks!
>
> --
> Russell Senior
> russell@...sonaltelco.net